1. Field of the Invention
This invention relates to a combination of an improved combustion chamber configuration and a dual spark-ignition internal combustion engine which is arranged to lower the emission level of nitrogen oxides by supplying a portion of the exhaust gases into the combustion chamber of the engine.
2. Description of the Prior Art
In connection with the control of nitrogen oxides (NOx) generated during the combustion carried out in the combustion chamber of an internal combustion engine, it has been proposed that a considerably large amount of the exhaust gases of the engine is supplied to the combustion chamber to mix with an air-fuel mixture inducted into the combustion chamber, and then the air-fuel mixture mixed with the exhaust gases is ignited with two spark plugs disposed in the combustion chamber. With this proposition, the combustion chamber volume alotted to one spark plug is decreased compared with a prior art arrangement in which only one spark plug is disposed in each combustion chamber. As a result, the time required for the combustion carried out in the combustion chamber is shortened and accordingly stable combustion is obtained even under the condition of which a considerably large amount of the exhaust gases is supplied to the combustion chamber. This stable combustion causes stable and smooth running of the engine. Of course, the generation of NOx in the combustion chamber is suppressed by lowering the maximum temperature of the combustion due to the supply of the considerably large amount of exhaust gases into the combustion chamber, and therefore NOx emission level is effectively lowered.
Now, the thus arranged engine is required to improve or further shorten the combustion time of the air-fuel mixture in the combustion chamber in order to achieve more stable and smooth running of the engine. To meet this requirement, suitable locations of two spark plugs must be found in consideration of the relationship with intake and exhaust valves, since the combustion chamber volume is not sufficiently large for the disposition of the spark plugs and the intake and exhaust valves.